I have a box with all my old handwritten letters from just before the Internet and email exploded. I rarely take it out, but when I do, it's kind of neat to show my niece and nephew.
(I do wonder if all the people who say "collect memories, not things" have more vivid, eidetic memories than I do; mine can be a little fragmentary without help.)
I began doing this when my kids started school and would bring home new art every day. I love that they made a portrait of me by gluing macaroni to a paper plate then covering it in glitter, but I don't necessarily want to become the caretaker of that masterpiece forever.
"That's great Jimmy! Now let me get my camera..."
SNAP!
"There, now we've got that memory forever. Now open the trash can and throw it away!"
I know you don't literally do this, but that's what your comment made me think and it gave me a chuckle. How long do you usually hold on to them?
There was no rigid routine. Things would go in a pile and periodically the pile would go to the recycling bin.